Multi-probe gauge for slab characterization

ABSTRACT

The present subject matter at-least provides an apparatus for characterization of a slab of a material. The apparatus comprises a plurality of frequency-domain optical-coherence tomography (FD-OCT) probes configured for irradiating the slab of material at at-least one location, and detecting radiation reflected from the slab of material or transmitted there-through. Further, a centralized actuation-mechanism is connected to the plurality of OCT probes for simultaneously actuating one or more elements in each of said OCT probes to at-least cause a synchronized detection of the radiation from the slab of material. A spectral-analysis module is provided for analyzing at least an interference pattern with respect to each of said OCT probes to thereby determine at least one of thickness and topography of the slab of the material.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/914,445, filed Mar. 7, 2018, now U.S. Pat. No. 10,209,058, andincorporated herein by reference in its entirety. This application isalso related to U.S. patent application Ser. No. 15/410,328 filed onJan. 19, 2017, and incorporated herein by reference in its entirety.

TECHNICAL FIELD

The embodiments discussed in this disclosure are related to amulti-probe gauge for slab characterization.

BACKGROUND

Frequency domain based optical coherence tomography (FD-OCT) probes havebeen used for characterization of properties of slabs of materials suchas slab-thickness, slab structure and topography of the slabs. Forultra-thin slabs, industrially used measurement metrology is based onlow-coherence interferometry. Such techniques are based upon an analysisof reflected infrared photon flux arriving from slab surfaces(layer-interfaces). The slab-thickness and characterization of the slablayer structure is obtained by analysis of an interferogram resultingfrom the FD-OCT probes.

A parameter that is often considered during metrology is a throughputmeasured in ‘number of slabs’ a tool can measure in a unit of time(usually expressed in slabs per hour). However, the throughput of thetool-measuring slabs is limited in the case of FD-OCT probes at-leastdue to limitations within the existing slab-handling anddata-acquisition techniques. More specifically, data-acquisition speedis limited by the speed at which spectra can be acquired, which is inturn limited at least owing to independent operation of the plurality ofprobes positioned around the slab of material. In addition,conventional-mechanisms based on FD-OCT probes fail to take into accountinfluence of vibration of the slab of material during the process ofslab-characterization.

The subject matter claimed in this disclosure is not limited toembodiments that solve any disadvantages or that operate only inenvironments such as those described above. Rather, this background isonly provided to illustrate one example technology area where someembodiments described in this disclosure may be practiced.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified format that are further described in the detailed descriptionof the present disclosure. This summary is neither intended to identifykey or essential inventive concepts of the disclosure, nor is itintended for determining the scope of the invention or disclosure.

In one embodiment, the present subject matter provides an apparatus forcharacterization of a slab of material. The apparatus comprises aplurality of frequency-domain optical-coherence tomography (OCT) probesconfigured to irradiating the slab of material at at-least one location,and detecting radiation reflected from the slab of material ortransmitted there-through. Further, a centralized actuation-mechanism isconnected to the said plurality of OCT probes for actuating one or moreelements in each of the OCT probes at a same time during irradiation ofthe slab of material to cause a synchronized-detection of the radiationfrom the slab of material by the plurality of OCT probes. Aspectral-analysis module is configured to analyze an interferencepattern of the radiation detected by each of the OCT probes to therebydetermine at least one of thickness and topography of the slab ofmaterial.

In another embodiment, the present subject matter describes a method forcharacterization of a slab of material. The method comprises thepositioning the slab of material on a chuck. The slab of material isirradiated at at-least one location by a plurality of frequency-domainoptical-coherence tomography (OCT) probes. One or more elements withinthe plurality of OCT probes are actuated at a same time during theirradiation of the slab of material by the plurality of OCT probes tocause a synchronized detection of radiation reflected from the slab ofmaterial or transmitted there-through. Further, at least an interferencepattern of the radiation detected by each of said OCT probe isspectrally analyzed for determining thickness with respect to one ormore locations at the slab of material, and topography of the slab ofmaterial.

Overall, the present subject matter employs multiple synchronized FD-OCTprobes to achieve an increased-throughput of a tool configured tocharacterize slab properties and reduce the influence of vibration overthe results of measurement at-least due to a fast handling mechanism forthe slab of material.

To further clarify advantages and features of the invention claimedherein, example descriptions and embodiments are rendered by referenceto specific embodiments thereof, which is illustrated in the appendeddrawings. It is appreciated that these drawings depict only exampleembodiments of the invention and are therefore not to be consideredlimiting of its scope. The disclosure will be described and explainedwith additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an example representation of system within a probeoperating as a frequency domain optical coherence tomography (FD-OCT)probe;

FIG. 2 illustrates a second example representation of a system withinthe probe operating as the FD-OCT probe;

FIG. 3 illustrates a third example representation of a system within theprobe operating as the FD-OCT probe;

FIG. 4 illustrates an example beam-assembly that may be implementedwithin the systems of FIG. 1-3;

FIG. 5 illustrates a fourth example representation of a system withinthe probe acting as the FD-OCT probe;

FIG. 6 illustrates a system comprising synchronized multiple FD-OCTprobes for simultaneous measurement of properties of a slab of material;

FIG.7 illustrates a symmetric arrangement of two FD-OCT probes formeasurement of the transparent and nontransparent slabs of materials forreduction of the noise caused by vertical mechanical vibration of a slabof material;

FIG.8 illustrates a type of asymmetric arrangement of two FD-OCT probesresulting from the relative motion of the slab of material with respectto probes due to vibration during the first portion of the vibrationwith respect to the slab of material;

FIG.9 illustrates another type of asymmetric arrangement of two FD-OCTprobes with respect to the slab of material, resulting from motion ofthe slab of material due to vibration during the second portion ofvibration cycle shown in FIG. 8;

FIG.10 illustrates occurrence of error during a slab-thicknessmeasurement in case of the arrangement of the FD-OCT probes as depictedin FIG. 8 and FIG. 9 resulting from the vibratory-motion of the slab ofmaterial with respect to the FD-OCT probes;

FIG. 11 illustrates synchronized FD-OCT probes utilizing aspectrometer-detector combination for measurement of properties of aslab of material;

FIG. 12 illustrates operation of a spectrometer-detector combination asconnected to the synchronized FD-OCT probes;

FIG. 13 illustrates synchronized FD-OCT probes utilizing aspectrometer-detector combination through an optical-switch formeasurement of properties of the slab of material;

FIG. 14 illustrates a flowchart of an example method of measurement ofproperties of the slab of material through synchronized FD-OCT probes;and

FIG. 15 illustrates a computing device configured to facilitatemeasurement of properties of a slab of material through synchronizedFD-OCT probes.

The elements in the drawings are illustrated for simplicity and may nothave been necessarily been drawn to scale. Furthermore, in terms of theconstruction of the device, one or more components of the device mayhave been represented in the drawings by conventional symbols, and thedrawings may show only those specific details that are pertinent tounderstanding the embodiments of the present disclosure so as not toobscure the drawings with details that will be readily apparent to thoseof ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the present disclosure is thereby intended, suchalterations and further modifications in the illustrated system, andsuch further applications of the principles of the present disclosure asillustrated therein being contemplated as would normally occur to oneskilled in the art to which the present disclosure relates.

The foregoing general description and the following detailed descriptionare explanatory of the present disclosure and are not intended to berestrictive thereof

Reference throughout this specification to “an aspect”, “another aspect”or similar language means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present disclosure. Thus, appearancesof the phrase “in an embodiment”, “in another embodiment” and similarlanguage throughout this specification may, but do not necessarily, allrefer to the same embodiment.

The terms “comprises”, “comprising”, or any other variations thereof,are intended to cover a non-exclusive inclusion, such that a process ormethod that comprises a list of steps does not include only those stepsbut may include other steps not expressly listed or inherent to suchprocess or method. Similarly, one or more devices or sub-systems orelements or structures or components proceeded by “comprises . . . a”does not, without more constraints, preclude the existence of otherdevices or other sub-systems or other elements or other structures orother components or additional devices or additional sub-systems oradditional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this present disclosure belongs. The system, methods,and examples provided herein are illustrative only and not intended tobe limiting.

Embodiments of the present disclosure will be described below in detailwith reference to the accompanying drawings.

FIG. 1 illustrates an example representation of a system 100 orarrangement within a probe operating as a frequency domain opticalcoherence tomography (FD-OCT) probe for measuring one or more propertiesof a slab of material 102. In some embodiments, the slab of material 102may be any suitable piece of material that may have a relatively flatsurface. For example, the slab of material 102 may be a silicon wafer, asemiconductor wafer, a glass plate or glass sheet (e.g., glass sheetsused for wafer carriers, windows, flat panel displays, etc.), apolyester sheet (e.g., used for flexible panel displays), a polyimidesheet (e.g., used for flexible panel displays), sheet metal, a sandwichof various materials, such as those discussed above, or any otherrelatively flat element in which measuring properties of the elementsuch as thickness or topography may be performed. A description andexample of the system 100 can also be found at-least with respect toembodiments defined under FIG. 1 of the U.S. patent application Ser. No.15/410328, filed Jan. 19, 2017, the complete-disclosure of which isincorporated herein by reference in its entirety.

The system 100 configured to inspect the slab of material 102 isarranged within the FD-OCT probe and accordingly denotes an internalassembly. In general, the system 100 may be configured to inspect theslab of material 102 in order to determine one or more properties of theslab of material 102 such as, for example, a thickness 106 of the slabof material 102 and a topography of a front surface 104 and/or a backsurface 105 of the slab of material 102. To perform the inspection, thesystem 100 may include single mode optical fibers 108, 110, 112, and114, a broadband light source 116, a beam forming assembly 118, adirectional element 126, and an etalon filter 120 and a spectrometer 122both controlled by a computer 124.

The broadband light source 116 may be configured to emit light over theoptical fiber 108. The directional element 126 may be configured toreceive the light from the broadband light source 116 over the opticalfiber 108 and direct the light to the beam assembly 118 over the opticalfiber 110. The beam assemblyl18 may be configured to receive the lightover the optical fiber 110 and direct the light toward the slab ofmaterial 102, i.e. irradiate the slab of material 102. The beam assembly118 may be further configured to receive the light reflected from theirradiated slab of material 102 and direct the light back to thedirectional element 126 over the optical fiber 110. The etalon filter120, as controlled by the computer 124, may be configured to receive thelight over the optical fiber 112 after the light has been reflected fromthe slab of material 102, filter the light, and direct the light overthe optical fiber 114. The spectrometer 122, as controlled by thecomputer 124, may be configured to receive the light over the opticalfiber 114, after the light has been filtered by the etalon filter 120and after the light has been reflected from the slab of material 102,and spectrally analyze the light. More specifically, the spectrometer122 may be coupled to one-dimensional array-detector (e.g. a chargecoupled device) to capture electric-charge corresponding to aninterference pattern (e.g., an interferogram) formed due to interferenceamong the diffracted-frequencies due to dispersion of reference andreflected light within the spectrometer 122. The interferogram asobtained from the array-detector is used for spectral-analysis of thereflected-light from the slab of material 102. In some examples, the onedimensional array detector may be in-built within the spectrometer 122.

The spectral analysis of the light may include determining topography ofthe front surface 104 and/or the back surface 105 of the slab ofmaterial 102 and/or determining the thickness 106 of the slab ofmaterial 102. For such purposes, the computer 124 may be electricallycoupled to the etalon filter 120 and to the spectrometer 122, andoperates as a spectral-analysis module. The computer 124 may beconfigured to determine the thickness 106 of the slab of material 102and/or determining a topography of the front-surface 104 the backsurface 105 of the slab of material 102.

The computing-device 124 executes instructions to perform operationswith respect to the spectrometer 122 in order to determine a topographyof the front surface 104 and/or the back surface 105 of the slab ofmaterial 102 and/or determine the thickness 106 of the slab of material102. In an example, the instructions to measure the thickness 106 of theslab of material 102 correspond to the following sequential-procedure asillustrated with respect to FIG. 1 in U.S. patent application Ser. No.15/410328:

-   -   1. Measurement of the reference spectrum (as shown in FIG. 9A of        U.S. patent application Ser. No. 15/410328) of the broadband        light source 116    -   2. Measurement the signal spectrum (as shown in FIG. 9B of U.S.        patent application Ser. No. 15/410328) of the light reflected        from the slab of material 102 having a known refractive index n,        and passing through the etalon filter 120 having a known        thickness which is known to be slightly larger than the        thickness 106 of the measured slab of material 102.    -   3. Calculating a normalized spectrum (as shown in FIG. 9C of        U.S. patent application Ser. No. 15/410328) by dividing the        signal spectrum by the reference spectrum.    -   4. Calculating the frequency Ω of observed oscillations in the        normalized spectrum.    -   5. Calculating the thickness 106 of the slab of material 102        using Equation 34 of U.S. patent application Ser. No. 15/410328.

The topography of the front surface 104 of the slab of material 102 maybe determined by placing the slab of material 102 on an XY motion stageperpendicular to light beam impinging front surface 104, wherein thefront surface 104 is parallel to plane of motion of XY stage, and bycollecting a data-set comprising the data set on a large number Mcomprising the x_(j) and y_(j) coordinates of the point where the beamis impinging the front surface 104 of the slab of material 102 and thedistance between the a stationary lens (shown in FIG. 4 as 404) of thebeam-forming assembly 118 and the front surface 104 of the slab ofmaterial 102 z_(j), where j=1 . . . M. The set of points (x_(j), y_(j),z_(j)) can then be used to construct a three dimensional map of thefront surface 104 of the slab of material 102. A similar procedure maybe performed to determine the topography of the back surface 105 of theslab of material 102.

FIG. 2 illustrates another example system 200 or arrangement within theone probe operating as the FD-OCT probe for inspecting a slab ofmaterial. A description and example of the system 200 may also be foundat least with respect to embodiment defined under FIG. 2 of theaforesaid U.S. patent application Ser. No. 15/410328.

The system 200, in addition to components referred with the system 100,further includes a second directional element 213, an etalon filter 220,and a single mode optical fiber 215. The second directional element 213may be configured to receive the light from the directional element 126over the optical fiber 112 and direct the light to the etalon filter 220over the optical fiber 215. The etalon filter 220 may be configuredsimilarly to the etalon filter 120 of FIG. 1, except that the etalonfilter 220 may be configured to receive the light from the seconddirectional element 213 over the optical fiber 215 after the light hasbeen reflected from the irradiated slab of material 102 and direct thelight back to the second directional element 213 over the optical fiber215. The spectrometer 122 of the system 200 may then be configured toreceive the light from the second directional element 213 over theoptical fiber 114.

FIG. 3 illustrates a third example representation of a system 300,within the probe operating as the FD-OCT probe, for inspecting the slabof material, arranged in accordance with at least some embodimentsdescribed in this disclosure. An example description of the system 300may also be found at least with respect to embodiment defined under FIG.3 of the aforesaid U.S. patent application Ser. No. 15/410328.

The system 300, in addition to elements in common with the system 100,may include a single mode optical fiber 317 and an etalon filter 320.The etalon filter 320 may be configured similarly to the etalon filter120 of FIG. 1, except that the etalon filter 320 may be configured toreceive the light over the broadband light source 116 over the opticalfiber 317 before the light is directed toward the slab of material 102and then, after filtering the light, direct the light over the opticalfiber 108 to the directional element 126. Then, after the light has beenreflected from the slab of material 102, the spectrometer 122 may beconfigured to receive the light from the directional element 126 overthe optical fiber 112.

FIG. 4 illustrates an example beam assembly 400 containing a referenceplane enabling absolute distance metrology, arranged in accordance withat least some embodiments described in this disclosure and implementablewithin the systems of FIG. 1-3 of the present subject matter. An exampledescription of the assembly 400 can also be found at least with-respectto a beam-assembly 500, as defined under FIG. 5 within the aforesaidU.S. patent application Ser. No. 15/410328.

The beam assembly 400 may be employed as the beam assembly 118 in thesystems 100, 200 and 300 of FIG. 1 till FIG. 3. The beam assembly 400may include lenses 402 and 404. The beam assembly 400 may alsooptionally include a beam splitter 406 and a reflector 408. The lens 402may be configured to receiving the light over the optical fiber 110 andcollimate and direct the light toward the beam splitter 406. The beamsplitter 406 may be configured to split the light from the lens 402 intofirst and second portions, direct the first portion of the light towardthe lens 404, and direct the second portion of the light onto areflector 408. The lens 404 may be configured to receive the firstportion of the light from the beam splitter 406, direct the firstportion of the light toward the slab of material 102, and direct thefirst portion of the light after being reflected from the slab ofmaterial back toward the beam splitter 406. Further, the reflector 408may be configured to receive the second portion of the light from thebeam splitter 406 and reflect the second portion of the light backtoward the beam splitter 406. The beam splitter 406 may be furtherconfigured to combine the first portion of the light after beingreflected from the slab of material 102 and the second portion of thelight after being reflected from the reflector 408, and then direct thecombined light toward the lens 402. Finally, the lens 402 may beconfigured to receive the combined light and direct the combined lightover the optical fiber 110.

The beam assembly 400 may be employed to gauge the optical pathdifference (OPD) between the first portion of the light and the secondportion of the light, which can be used to measure the distance betweenthe front surface 104 of the slab of material 102 and the lens 404. Ashas been depicted with respect to the description in FIG. 1, distancebetween the front surface 104 of the slab of material 102 and the lens404 assists in determination of topography of front and back surfaces ofthe slab of material 102.

FIG. 5 illustrates a fourth example system 500 within the FD-OCT probefor inspecting a slab of material, in accordance with at least someembodiments described in this disclosure. An example description of saidsystem 500 can also be found at least with-respect to the system asdefined under FIG. 4 of the aforesaid U.S. patent application Ser. No.15/410328.

Although the beam splitter 406 and the reflector 408 may be beneficialin some embodiments of the beam assembly 400 as noted above with respectof FIG. 4 of the present subject matter, the present FIG. 5 omits thebeam splitter 406 and the reflector 408. For example, in addition toelements in common with the system 100, the system 500 may include afirst beam assembly 518a and a second beam assembly 518. Since the lightonly passes through the beam assemblies 518a and 518b in a singledirection in the system 500, the beam splitter 406 and the reflector 408(otherwise present in FIG. 4 of the present subject matter) may beomitted.

More specifically, the beam assembly 518 a may be similar to the beamassembly 118 of FIG. 1 except that the beam-assembly 518 a is notconfigured to receive the light reflected back from the slab of material102. Instead, the light directed from the beam assembly 518 a istransmitted through the slab of material 102 toward the second beamassembly 518 b. The second beam assembly 518 b may be configured toreceive the light transmitted through the slab of material 102 anddirect the light to the etalon filter 120 over the optical fiber 112.The etalon filter 120 may then be configured to receive the light fromthe second beam assembly 518 b over the optical fiber 112 after thelight has been transmitted through the slab of material 102.Accordingly, the characterization of the slab of material 102 in thepresent FIG. 5 is based on light transmitted through the slab ofmaterial 102.

FIG. 6 illustrates a system 600 comprising multiple synchronized FD-OCTprobes for simultaneous measurement of properties of a slab of material.More specifically, FIG. 6 describes multiple probes 602(1) . . . 602(n)for acquiring data synchronously for measurement of thickness andtopography of the slabs of material. The assembly of each of said FD-OCTprobe 602(1 to n) within the system 600 corresponds to the systems 100,200, 300 and 500 as have been referred in the previous figures, whereineach of the probe 602 is an assembly of single mode optical fibers 108,110, 112, 215, 317 and 114, the broadband light source 116, the beamforming assembly 118, the directional elements 126, 213, the etalonfilter 120, 320 and the spectrometer 122. Further, all of the FD-OCTprobes 602 in the system 600 measure a common slab of material 102 andconnected to the common spectral-analysis module or the computing system124. For sake of brevity, only two FD-OCT probes 602(1) and 602(n) havebeen shown as a part of the system 600.

Within the present system 600, the upper FD-OCT probe 602(1) issynchronized with lower FD-OCT probe 602(n) by means of a centralizedactuation mechanism 2000 or a common electrical-cable 2000 whose one endis connected to all the FD-OCT probes. The other end of suchelectrical-cable 2000 is connected to a triggering source (e.g. amicrocontroller) that sends pulses to actuate each of said FD-OCT probesat the same time such that the FD-OCT probes simultaneously detect thereflected radiation from the slab of material 102 and thereby enable asimultaneous measurement of distances from the slab of material 102 toeach of the FD-OCT probes. In the present disclosure, reference tooperations happening “simultaneously” or “at the same time” or being“synchronized” allows for margins of error in the simultaneous natureof, that may be less than 1%, 5%, or 10% depending on variousimplementation or materials constraints. Accordingly, upon havingreceived a trigger through the electrical cable 2000, each of the probeout of the plurality of FD-OCT probes 602(1 to n) operatessimultaneously. In other example, the actuation mechanism 2000 may beelectro-mechanical, opto-electrical or opto-mechanical in nature.Largely, the simultaneous operation of the each of the probe 602 may bedefined as a sequential-operation of:

-   -   a) irradiating the slab of material at a particular location;    -   b) detecting radiation reflected from the slab of material or        transmitted there-through;

Further, as may be understood with respect to FIG. 6, each of pluralityof the probes 602(1 to n), inter alia, includes a combination ofspectrometer 122 and uni-dimensional array detector 124. In other words,each of the probes 602 includes a respective spectrometer-array detectorcombination, wherein the spectrometer and array detector may either beintegrated or separate from each other.

FIG. 7 illustrates a symmetric arrangement of two FD-OCT probes formeasurement of the transparent and nontransparent slabs of materials forreduction of the noise caused by vertical mechanical vibration of a slabof material. More specifically, FIG. 7 illustrates the system 600 ofFD-OCT probes for the purposes of reducing the influence of mechanicalvibrations of the slab of material 102 during the course of determiningthickness of the slab of material 102, which may be transparent,semi-transparent, or non-transparent in nature. As shown in FIG. 7, thesystem 600 comprises a pair of probes 602(1) and 602(2). ‘D’ representsa distance between the two probes 602(1) and 602(2) that may bepre-determined through any known means. Further, the distances H1 andH2, respectively depict the distance of the slab of material 102 fromthe first probe 602(1) and the second probe 602(2). Said distances aredetermined based on the spectral analysis performed with respect to eachof the probe 602(1) and 602(2), as illustrated through the procedureillustrated in FIG. 1. Thereafter, the thickness ‘t’ of the slab ofmaterial 102 is determined based on following criteria (as illustratedin U.S. Pat. No. 7,116,429):

t=D−H1−H2

The simultaneous calculation of H1 and H2 owing to a synchronizedoperation of the probe 602(1) and 602(2) coupled with a symmetricarrangement of probes 602(1) and 602(2) with respect to the slab ofmaterial 102 causes a precise determination of distances H1 and H2 andthereby a precise determination of the thickness ‘t’. Such measurementovercomes the influence of mechanical vibrations of the slab of material102 during the course of determining thickness of the slab of material102.

FIG. 8 illustrates a type of asymmetric arrangement of two FD-OCT probesresulting from the relative motion of the slab of material with respectto probes due to vibration during the first portion of the vibrationwith respect to the slab of material.

On the other hand, FIG.9 illustrates another type of asymmetricarrangement of two FD-OCT probes with respect to the slab of material,resulting from motion of the slab of material due to vibration duringthe second portion of vibration cycle shown in FIG. 8.

Both FIG. 8 and FIG. 9 illustrate a non-synchronized arrangement of theprobes 602(1) and 602(2), as a result of which both probes determine thedistance from the slab of material 102 at different instants of time,say at t1 and t2, respectively. As illustrated in FIG. 8, at time ‘t1’,the distance between probe 602(1) and the slab of material 102 isobserved to be H1A. As illustrated in FIG. 9, at time ‘t2’, the distancebetween probe 602(2) and the slab of material 102 is observed to be H2A.The asymmetric arrangement of two FD-OCT probes as depicted in FIG. 8and FIG. 9 result from the relative motion of the slab of material withrespect to probes due to vibration upwards and downwards, respectively.Such upward and downward vibration may also be referred as first andsecond portion of the vibration or vibratory-motion. Based on saidreadings, the thickness ‘tA’ gets determined as follows:

tA=D−H1A−H2A

FIG.10 illustrates occurrence of error during a slab-thicknessmeasurement in case of the arrangement of the FD-OCT probes as depictedin FIG. 8 and FIG. 9 resulting from the vibratory-motion of the slab ofmaterial with respect to the FD-OCT probes. Clearly, as indicated inFIG. 10, thickness ‘tA’ is substantially greater than the actualthickness ‘t’ of the slab of material 102 and gets determined as asubstantially high thickness of the slab of material 102 owing to acontinuous-vibration of the slab of material 102 with respect to theprobes along y axis and non-synchronized operation of the probes 602(1)and 602(2). Accordingly, as may be understood, the synchronizedoperation of the probes 602(1) and 602(2) is able to determine theprecise thickness ‘t’ despite the vibration of the slab of material 102by virtue of measurement of the distances H1 and H2 as the same instantof time.

FIG. 11 illustrates synchronized FD-OCT probes utilizing aspectrometer-detector combination for measurement of properties of aslab of material. More particularly, the system 1100 depicted in FIG. 11has synchronized FD-OCT probes 602 utilizing a centralized or solespectrometer-detector combination for measurement of thickness andtopography of slabs of material. More specifically, neither of theFD-OCT probes 602 in the system 1100 comprises an in-built spectrometerand detector combination. Instead, each of the probes 602 is ratheraligned to a centralized spectrometer 1102 and detector 1104, therebyincurring significantly lower manufacturing costs when compared with thesystem 600. Further, the detector 1104 within the system is a 2dimensional (2D) array detector, e.g., a charge coupled device havingmultiples rows of photo-sensitive elements.

FIG. 12 illustrates operation of a spectrometer-detector combination asconnected to the synchronized FD-OCT probes. The spectrometer 1102 asillustrated in FIG. 12 is a dispersive-element based spectrometer. Asshown in the figure, the light 1208, 1210 arriving from the slab ofmaterial 102 is directed to a same entrance slit 1202 of the dispersivespectrometer 1102 and accordingly positioned in separate locations alongthe entrance slit 1202, or in other words at different locations withinan object-plane of spectrometer 1102. Upon having undergone diffractionfrom a dispersive element i.e. grating 1204 of the spectrometer 1102, aplurality of dispersed images of the slit 1202 are projected on thetwo-dimensional array detector 1104.

The light entering through the different points on the same slit 1202form spectral lines across the detector 1104, such that each row (i.e. auni-dimensional array) of light sensitive elements corresponds to aparticular spectral line or spectrum out of the plurality of spectrumscaptured by the detector 1102. More specifically, each light originatingfrom the slab of material 102 undergoes dispersion to produce aplurality of diffracted wavelengths that interfere with one another toproduce a corresponding interferogram with respect to a particularlight. Overall, a plurality of interferograms are captured as aplurality of spectral lines through the array detector 1102. The voltagesignal corresponding to various spectral lines (i.e. each row of thearray-detector) is multiplexed and thereafter digitized forserial-transmission through a cable to computer 124 (i.e. spectralanalysis module) that further analyzes spectra in accordance with the‘procedure’ as described within the description of FIG. 1. Accordingly,each spectral-line corresponding to each light received from probe 602(1to n) is analyzed separately through spectral analysis module.

FIG. 13 illustrates synchronized FD-OCT probes utilizing aspectrometer-detector combination through an optical-switch formeasurement of properties of the slab of material. A system 1300 asshown in FIG. 13 comprises synchronized FD-OCT probes utilizing thecentralized spectrometer and detector combination (as depicted throughFIG. 11) through an optical-switch 1302 for measurement of thickness andtopography of the slab of material. More specifically, each of theplurality of probes 602(1 to n) are ported to the centralizedspectrometer 1102 through an optical-switch 1304. In addition, saidoptical switch 1304 may be also appropriated to link a single broadbandlight source to the multiple probes 602(1 to n) for the purposes ofirradiating the slab of material 102. In an example, the optical switchmay correspond to either 1×N or N×1 configuration and may exemplarily bemechanical switch or Micro-electromechanical System (MEMS) switch.

FIG. 14 illustrates a flowchart of an example-method of measurement ofproperties (e.g. thickness and topography) of a slab of material throughmultiple FD-OCT probes 602(1 to n).

At step 1402, the slab of material 102 to be measured in placed within achuck for initiating the measurement.

At step 1404, one or more elements within a plurality of FD-OCT probes602(1 to n) are actuated at the same time by the centralized actuatingmechanism 2000 to cause an operation thereof. Such operation of theplurality of probes 602 is achieved due to simultaneous actuation ofeach of the probe 602 by the actuation mechanism as described withrespect to FIG. 6 to FIG. 11 and comprises:

-   -   a) irradiating the slab of material at-least one location by        said plurality of probes 602; and    -   b) synchronously detecting by the plurality of probes 602 the        radiation reflected from the slab of material or transmitted        there-through.

The synchronized-operation of the probes 602 in step 1404 furthercomprises filtering the detected radiation through an etalon-filter 120,220, 320 present within each of the FD-OCT probe 602 to cause generationof the interference pattern with respect to each FD-OCT probe 602. Anindividual operation of each of the FD-OCT probe 602 corresponds to themethod-steps as described with respect to the FIG. 10 of the aforesaidUS patent application Ser. No. 15/410328. Further, the radiation orlight outputted from each of the FD-OCT probe 602 is dispersed by adispersive element (e.g. grating) within the spectrometer 122, 1102 tothereby generate a plurality of spectrums. Each of the plurality ofspectrums detected through the 2-dimensional array-detector 1104thereafter undergo a spectral-analysis through the next step 1406. Inorder to facilitate such spectral-analysis, a plurality of signals (e.g.voltage) corresponding to the detected-spectrums and generated at thedetector are multiplexed and thereafter digitized for transmission tothe computer 124. The digitized-signal received at the computer 124thereafter undergoes a digital to analog conversion through adigital-to-analog converter and de-multiplexing to recreate a pluralityof analog signals at the computer 124 for the purposes ofspectral-analysis.

At step 1406, the analog-signal(s) recreated at the computer 124 fromthe previous step 1404 are spectrally analyzed (in accordance with theprocedure as described with respect to FIG. 1). Accordingly, the presentstep denotes a spectral-analysis of the interference pattern or spectrumcorresponding to each of the probes. The spectral analysis in turn leadsto a determination of properties of the slab of material such as a)thickness with respect to one or more locations at the slab of material;and b) topography of the slab of material.

FIG. 15 shows yet another example implementation in accordance with theembodiment of the present disclosure by depicting a computing deviceconfigured to facilitate measurement of properties of a slab of materialthrough synchronized FD-OCT probes. More specifically, the presentfigure illustrates an example hardware configuration of the computersystem 124 as a computing system 1500. The computer system 1500 caninclude a set of instructions that can be executed to cause the computersystem 1500 to perform any one or more of the methods disclosed. Thecomputer system 1500 may operate as a standalone device or may beconnected, e.g., using a network, to other computer systems orperipheral devices.

In a networked deployment, the computer system 1500 may operate in thecapacity of a server or as a client user computer in a server-clientuser network environment, or as a peer computer system in a peer-to-peer(or distributed) network environment. The computer system 1500 can alsobe implemented as or incorporated across various devices, such as apersonal computer (PC), a tablet PC, a personal digital assistant (PDA),a mobile device, a palmtop computer, a laptop computer, a desktopcomputer, or any other machine capable of executing a set ofinstructions (sequential or otherwise) that specify actions to be takenby that machine. In an example implementation, the computer system 1500may be a mobile computing cum display device capable of being used by auser. Further, while a single computer system 1500 is illustrated, theterm “system” shall also be taken to include any collection of systemsor sub-systems that individually or jointly execute a set, ormultiple-sets, of instructions to perform one or more computerfunctions.

The computer system 1500 may include a processor 1502 e.g., a centralprocessing unit (CPU), a graphics processing unit (GPU), or both. Theprocessor 1502 may be a component in a variety of systems. For example,the processor 1502 may be part of a standard personal computer or aworkstation. The processor 1502 may be one or more general processors,digital signal processors, application specific integrated circuits,field programmable gate arrays, servers, networks, digital circuits,analog circuits, combinations thereof, or other now known or laterdeveloped devices for analyzing and processing data The processor 1502may implement a software program, such as code generated manually (i.e.,programmed).

The computer system 1500 may include a memory 1504, such as a memory1504 that can communicate via a bus 1508. The memory 1504 may include,but is not limited to computer readable storage media such as varioustypes of volatile and non-volatile storage media, including but notlimited to random access memory, read-only memory, programmableread-only memory, electrically programmable read-only memory,electrically erasable read-only memory, flash memory, magnetic tape ordisk, optical media and the like. In one example, the memory 1504includes a cache or random access memory for the processor 1502. Inalternative examples, the memory 1504 is separate from the processor1502, such as a cache memory of a processor, the system memory, or othermemory. The memory 1504 may be an external storage device or databasefor storing data. The memory 1504 is operable to store instructionsexecutable by the processor 1502. The functions, acts or tasksillustrated in the figures or described may be performed by theprogrammed processor 1502 executing the instructions stored in thememory 1504. The functions, acts or tasks are independent of theparticular type of instructions set, storage media, processor orprocessing strategy and may be performed by software, hardware,integrated circuits, firm-ware, micro-code and the like, operating aloneor in combination. Likewise, processing strategies may includemultiprocessing, multitasking, parallel processing and the like.

As illustrated, the computer system 1500 may or may not further includea touch-sensitive display unit 1510, for outputting determinedinformation as well as receiving a user's touch-gesture based inputs,such as drag and drop, single tap, multiple-taps, etc. The display 1510may act as an interface for the user to see the functioning of theprocessor 1502, or specifically as an interface with the software storedin the memory 1504 or in the drive unit 1506.

Additionally, the computer system 1500 may include an input device 1512configured to allow a user to interact with any of the components ofsystem 1500. The computer system 1500 may also include a disk or opticaldrive unit 1506. The disk drive unit 1506 may include acomputer-readable medium 1518 in which one or more sets of instructions1514, e.g. software, can be embedded. Further, the instructions 1514 mayembody one or more of the methods or logic as described. In a particularexample, the instructions 1514 may reside completely, or at leastpartially, within the memory 1504 or within the processor 1502 duringexecution by the computer system 1500.

The present disclosure contemplates a computer-readable medium thatincludes instructions 1514 or receives and executes instructions 1514responsive to a propagated signal so that a device connected to anetwork 1526 can communicate voice, video, audio, images or any otherdata over the network 1526. Further, the instructions 1514 may betransmitted or received over the network 1516 via a communication portor interface 1520 or using a bus 1508. The communication port orinterface 1520 may be a part of the processor 1502 or may be a separatecomponent. The communication port 1520 may be created in software or maybe a physical connection in hardware. The communication port 1520 may beconfigured to connect with a network 1516, external media, the display1510, or any other components in computing system 1500, or combinationsthereof. The connection with the network 1516 may be establishedwirelessly as discussed later. Likewise, the additional connections withother components of the system 1500 may be established wirelessly. Thenetwork 1516 may alternatively be directly connected to the bus 1508.

The network 1516 may include wireless networks, Ethernet AVB networks,or combinations thereof. The wireless network may be a cellulartelephone network, an 802.11, 802.16, 802.20, 802.1Q or WiMax network.Further, the network 1516 may be a public network, such as the Internet,a private network, such as an intranet, or combinations thereof, and mayutilize a variety of networking protocols now available or laterdeveloped including, but not limited to TCP/IP based networkingprotocols. The system is not limited to operation with any particularstandards and protocols. For example, standards for Internet and otherpacket switched network transmission (e.g., TCP/IP, UDP/IP, HTML, HTTP)may be used.

The present subject matter comprising multiple FD-OCT probes forcharacterization of one or more properties of a slab of material,at-least enables a substantially high data-acquisition speed throughsynchronized FD-OCT probes, i.e. through measuring the distances betweenthe probes and slab at the same instant of time. This in turnsuccessfully overcomes the influence of vibration of the slab ofmaterial during the process of slab-characterization, which may includethe determination of one or more properties of the slab of material asdiscussed above. Moreover, the present subject matter provides a systemlow on manufacturing costs through employment of a centralizedspectrometer-detector combination.

While specific language has been used to describe the disclosure, anylimitations arising on account of the same are not intended. As would beapparent to a person in the art, various working modifications may bemade to the method in order to implement the inventive concept as taughtherein.

The drawings and the forgoing description give examples of embodiments.Those skilled in the art will appreciate that one or more of thedescribed elements may well be combined into a single functionalelement. Alternatively, certain elements may be split into multiplefunctional elements. Elements from one embodiment may be added toanother embodiment. For example, orders of processes described hereinmay be changed and are not limited to the manner described herein.

Moreover, the actions of any flow diagram need not be implemented in theorder shown; nor do all of the acts necessarily need to be performed.Also, those acts that are not dependent on other acts may be performedin parallel with the other acts. The scope of embodiments is by no meanslimited by these specific examples. Numerous variations, whetherexplicitly given in the specification or not, such as differences instructure, dimension, and use of material, are possible. The scope ofembodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any component(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or component of any or all the claims.

We claim:
 1. An apparatus for characterization of a slab of materialcomprising: a first frequency-domain optical-coherence tomography (OCT)probe configured to : irradiate the slab of material at a firstlocation; and detect first radiation reflected from the slab of materialat the first location in which the first radiation is reflected inresponse to irradiating the slab of material at the first location; asecond frequency-domain OCT probe configured to : irradiate the slab ofmaterial at a second location; and detect second radiation reflectedfrom the slab of material at the second location in which the secondradiation is reflected in response to irradiating the slab of materialat the second location; a centralized actuation mechanismcommunicatively coupled to the first OCT probe and the second OCT probeand configured to actuate the first OCT probe and the second OCT probeat a same time during irradiation of the slab of material at the firstlocation and at the second location to cause a synchronized detection ofthe first radiation by the first OCT probe and of the second radiationby the second OCT probe; and a spectral-analysis module configured toanalyze the first radiation reflected from the slab of material and thesecond radiation reflected from the slab of material to therebydetermine at least one of thickness and topography of the slab ofmaterial.
 2. The apparatus as claimed in claim 1, wherein the first OCTprobe comprises a beam forming assembly configured to: receive the firstradiation over an optical fiber from a radiation-source and direct thefirst radiation toward the slab of material; and detect the firstradiation reflected from the slab of material.
 3. The apparatus asclaimed in claim 2, wherein the first OCT probe comprises anetalon-filter in optical communication with the beam-forming assembly,the etalon-filter is configured to: receive the first radiation over theoptical fiber either before the first radiation is directed toward theslab of material or after the radiation has been reflected from the slabof material, filter the received first radiation to cause generation ofa first interference pattern, wherein the analyzing of the firstradiation reflected from the slab of material includes analyzing thefirst interference pattern.
 4. The apparatus as claimed in claim 1,wherein the first OCT probe further comprises: a spectrometer inoptical-communication with the etalon-filter and configured to dispersethe first radiation reflected from the slab of material to generate afirst spectrum; and a unidirectional array detector configured to detectthe first spectrum and trigger a spectral-analysis thereof by thespectral-analysis module such that the spectral analysis of the firstspectrum is included in the analysis of the first radiation reflectedfrom the slab of material.
 5. The apparatus as claimed in claim 1,further comprising a centralized spectrometer in optical-communicationwith the first OCT probe and configured to: disperse the first radiationoutput from the first OCT probe during irradiation of slab of materialby the first OCT probe to generate a first spectrum; and disperse thesecond radiation output from the second OCT probe during irradiation ofslab of material by the second OCT probe to generate a second spectrum;and a two-dimensional array detector configured to detect the firstspectrum and the second spectrum and trigger a spectral-analysis thereofsuch that the spectral analysis of the first spectrum is included in theanalysis of the first radiation reflected from the slab of material andsuch that the spectral analysis of the second spectrum is included inthe analysis of the second radiation reflected from the slab ofmaterial.
 6. The apparatus as claimed in claim 5, wherein thetwo-dimensional array detector includes: a first group ofradiation-detecting elements corresponding to the first OCT probe andconfigured to detect the first spectrum; and a second group ofradiation-detecting elements corresponding to the second OCT probe andconfigured to detect the second spectrum.
 7. The apparatus described inclaim 5, further comprising: a multiplexer connected to the arraydetector and configured to multiplex a first signal corresponding to thefirst spectrum with a second signal corresponding to the secondspectrum; and an analog to digital-converter configured to digitize thereceived multiplexed signal for transmission to the spectral-analysismodule.
 8. The apparatus as claimed in claim 1, wherein the firstlocation corresponds to a first side of the slab of material and thesecond location corresponds to a second side of the slab of material. 9.The apparatus as claimed in claim 1, wherein the first location and thesecond location are along a same line that runs perpendicular to andthrough the first side and the second side.
 10. The apparatus as claimedin claim 1, wherein the first location and the second location are on asame side of the slab of material.
 11. A method for characterization ofa slab of material comprising: positioning the slab of material on achuck; actuating a first frequency-domain optical-coherence tomography(OCT) probe such that the first OCT probe irradiates the slab ofmaterial at a first location and detects first radiation reflected fromthe slab of material at the first location in which the first radiationis reflected in response to irradiating the slab of material at thefirst location; actuating a second frequency-domain OCT probesimultaneously with the actuating of the first OCT probe such that thesecond OCT probe irradiates the slab of material at a second locationand detects second radiation reflected from the slab of material at thesecond location in which the second radiation is reflected in responseto irradiating the slab of material at the second location and secondradiation is detected synchronously with the detection of the firstradiation by the first OCT probe; and spectrally analyzing the detectedfirst radiation and the detected second radiation to determine at leastone of: thickness with respect to one or more locations at the slab ofmaterial; and topography of the slab of material.
 12. The method asclaimed in claim 11, further comprising filtering the detected firstradiation through an etalon-filter within the first OCT probe to causegeneration of a first interference pattern of the detected firstradiation, wherein spectrally analyzing the detected first radiationincludes spectrally analyzing the first interference pattern.
 13. Themethod as claimed in claim 12, further comprising: dispersing the firstradiation output from the first OCT probe during irradiation of slab ofmaterial by the first OCT probe to generate a first spectrum; anddispersing the second radiation output from the second OCT probe duringirradiation of slab of material by the second OCT probe to generate asecond spectrum; and detecting, by a two-dimensional array detector, thefirst spectrum and the second spectrum to trigger a spectral-analysisthereof such that the spectral analysis of the first spectrum isincluded in the analysis of the first radiation reflected from the slabof material and such that the spectral analysis of the second spectrumis included in the analysis of the second radiation reflected from theslab of material.
 14. The method as claimed in claim 13, wherein thetwo-dimensional array detector includes: a first group ofradiation-detecting elements corresponding to the first OCT probe andconfigured to detect the first spectrum; and a second group ofradiation-detecting elements corresponding to the second OCT probe andconfigured to detect the second spectrum.
 15. The method as claimed inclaim 13, further comprising: multiplexing a first signal correspondingto the first spectrum with a second signal corresponding to the secondspectrum; and digitizing the received multiplexed signal for spectralanalysis.
 15. The method as claimed in claim 11, wherein thesimultaneous actuation of the first OCT probe and the second OCT probeincludes simultaneously measuring a first distance between the slab ofmaterial and the first OCT probe and a second distance between the slabof material and the second OCT probe.
 16. The method as claimed in claim11, wherein the first location corresponds to a first side of the slabof material and the second location corresponds to a second side of theslab of material.
 17. The method as claimed in claim 11, wherein thefirst location and the second location are along a same line that runsperpendicular to and through the first side and the second side.
 18. Themethod as claimed in claim 11, wherein the first location and the secondlocation are on a same side of the slab of material.